Protic ruthenium complexes using the dihydroxybipyridine (dhbp) ligand combined with a spectator ligand (N,N = bpy, phen, dop, Bphen) have been studied for their potential activity vs. cancer cells and their photophysical luminescent properties. These complexes vary in the extent of π expansion and the use of proximal (6,6′-dhbp) or distal (4,4′-dhbp) hydroxy groups. Eight complexes are studied herein as the acidic (OH bearing) form, [(N,N)2Ru(n,n′-dhbp)]Cl2, or as the doubly deprotonated (O− bearing) form. Thus, the presence of these two protonation states gives 16 complexes that have been isolated and studied. Complex 7A, [(dop)2Ru(4,4′-dhbp)]Cl2, has been recently synthesized and characterized spectroscopically and by X-ray crystallography. The deprotonated forms of three complexes are also reported herein for the first time. The other complexes studied have been synthesized previously. Three complexes are light-activated and exhibit photocytotoxicity. The log(Do/w) values of the complexes are used herein to correlate photocytotoxicity with improved cellular uptake. For Ru complexes 1–4 bearing the 6,6′-dhbp ligand, photoluminescence studies (all in deaerated acetonitrile) have revealed that steric strain leads to photodissociation which tends to reduce photoluminescent lifetimes and quantum yields in both protonation states. For Ru complexes 5–8 bearing the 4,4′-dhbp ligand, the deprotonated Ru complexes (5B–8B) have low photoluminescent lifetimes and quantum yields due to quenching that is proposed to involve the 3LLCT excited state and charge transfer from the [O2-bpy]2− ligand to the N,N spectator ligand. The protonated OH bearing 4,4′-dhbp Ru complexes (5A–8A) have long luminescence lifetimes which increase with increasing π expansion on the N,N spectator ligand. The Bphen complex, 8A, has the longest lifetime of the series at 3.45 μs and a photoluminescence quantum yield of 18.7%. This Ru complex also exhibits the best photocytotoxicity of the series. A long luminescence lifetime is correlated with greater singlet oxygen quantum yields because the triplet excited state is presumably long-lived enough to interact with 3O2 to yield 1O2.
- Award ID(s):
- 2102461
- NSF-PAR ID:
- 10342536
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 157
- Issue:
- 1
- ISSN:
- 0021-9606
- Page Range / eLocation ID:
- 014301
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
ABSTRACT We report the synthesis, photochemical and biological characterization of two new Ru(II) photoactivated complexes based on [Ru(tpy)(Me2bpy)(L)]2+(tpy = 2,2':6',2''‐terpyridine, Me2bpy = 6,6'‐dimethyl‐2,2'‐bipyridine), where L = pyridyl‐BODIPY (pyBOD). Two pyBOD ligands were prepared bearing flanking hydrogen or iodine atoms. Ru(II)‐bound BODIPY dyes show a red‐shift of absorption maxima relative to the free dyes and undergo photodissociation of BODIPY ligands with green light irradiation. Addition of iodine into the BODIPY ligand facilitates intersystem crossing, which leads to efficient singlet oxygen production in the free dye, but also enhances quantum yield of release of the BODIPY ligand from Ru(II). This represents the first report of a strategy to enhance photodissociation quantum yields through the heavy‐atom effect in Ru(II) complexes. Furthermore, Ru(II)‐bound BODIPY dyes display fluorescence turn‐on once released, with a lead analog showing nanomolar EC50values against triple negative breast cancer cells, >100‐fold phototherapeutic indexes under green light irradiation, and higher selectivity toward cancer cells as compared to normal cells than the corresponding free BODIPY photosensitizer. Conventional Ru(II) photoactivated complexes require nonbiorthogonal blue light for activation and rarely show submicromolar potency to achieve cell death. Our study represents an avenue for the improved photochemistry and potency of future Ru(II) complexes.
-
ABSTRACT We report new ruthenium complexes bearing the lipophilic bathophenanthroline (BPhen) ligand and dihydroxybipyridine (dhbp) ligands which differ in the placement of the OH groups ([(BPhen)2Ru(n,n′‐dhbp)]Cl2with
n = 6 and 4 in 1Aand 2A, respectively). Full characterization data are reported for 1Aand 2Aand single crystal X‐ray diffraction for 1A. Both 1Aand 2Aare diprotic acids. We have studied 1A, 1B, 2A, and 2B(B = deprotonated forms) by UV‐vis spectroscopy and 1 photodissociates, but 2 is light stable. Luminescence studies reveal that the basic forms have lower energy3MLCT states relative to the acidic forms. Complexes 1Aand 2Aproduce singlet oxygen with quantum yields of 0.05 and 0.68, respectively, in acetonitrile. Complexes 1 and 2 are both photocytotoxic toward breast cancer cells, with complex 2 showing EC50light values as low as 0.50 μM with PI values as high as >200vs . MCF7. Computational studies were used to predict the energies of the3MLCT and3MC states. An inaccessible3MC state for 2Bsuggests a rationale for why photodissociation does not occur with the 4,4′‐dhbp ligand. Low dark toxicity combined with an accessible3MLCT state for1O2generation explains the excellent photocytotoxicity of 2. -
Abstract Ru(II) complexes were synthesized with π‐expanding (phenyl, fluorenyl, phenanthrenyl, naphthalen‐1‐yl, naphthalene‐2‐yl, anthryl and pyrenyl groups) attached at a 1
H ‐imidazo[4,5‐f ][1,10]phenanthroline ligand and 4,4′‐dimethyl‐2,2′‐bipyridine (4,4′‐dmb) coligands. These Ru(II) complexes were characterized by 1D and 2D NMR, and mass spectroscopy, and studied for visible light and dark toxicity to human malignant melanoma SK‐MEL‐28 cells. In the SK‐MEL‐28 cells, the Ru(II) complexes are highly phototoxic (EC50 = 0.2–0.5 µm ) and have low dark toxicity (EC50 = 58–230 µm ). The highest phototherapeutic index (PI) of the series was found with the Ru(II) complex bearing the 2‐(pyren‐1‐yl)‐1H ‐imidazo[4,5‐f ][1,10]phenanthroline ligand. This high PI is in part attributed to the π‐rich character added by the pyrenyl group, and a possible low‐lying and longer‐lived3IL state due to equilibration with the3MLCT state. While this pyrenyl Ru(II) complex possessed a relatively high quantum yield for singlet oxygen formation (Φ∆ = 0.84), contributions from type‐I processes (oxygen radicals and radical ions) are competitive with the type‐II (1O2) process based on effects of added sodium azide and solvent deuteration. -
The synthesis, photophysics, and electrochemiluminescence (ECL) of four water-soluble dinuclear Ir( iii ) and Ru( ii ) complexes (1–4) terminally-capped by 4′-phenyl-2,2′:6′,2′′-terpyridine (tpy) or 1,3-di(pyrid-2-yl)-4,6-dimethylbenzene (N^C^N) ligands and linked by a 2,7-bis(2,2′:6′,2′′-terpyridyl)fluorene with oligoether chains on C9 are reported. The impact of the tpy or N^C^N ligands and metal centers on the photophysical properties of 1–4 was assessed by spectroscopic methods including UV-vis absorption, emission, and transient absorption, and by time-dependent density functional theory (TDDFT) calculations. These complexes exhibited distinct singlet and triplet excited-state properties upon variation of the terminal-capping terdentate ligands and the metal centers. The ECL properties of complexes 1–3 with better water solubility were investigated in neutral phosphate buffer solutions (PBS) by adding tripropylamine (TPA) as a co-reactant, and the observed ECL intensity followed the descending order of 3 > 1 > 2. Complex 3 bearing the [Ru(tpy) 2 ] 2+ units displayed more pronounced ECL signals, giving its analogues great potential for further ECL study.more » « less